In recent years, fiber laser devices are used in machines for machining utilizing laser light and in medical devices such as a surgical knife utilizing laser light. A fiber laser device is a device in which pulsed laser light emitted by a laser oscillator (master oscillator: MO) is amplified by an optical fiber amplifier (power amplifier: PA) and the amplified laser light is output through an output end.
Unfortunately, in a fiber laser device having such a configuration, part of laser light output toward an object to be irradiated may be reflected by the irradiated object and input to the fiber laser device through the output end thereof or laser light may be reflected at the output end. In such cases, the reflected laser light may be amplified again by the optical fiber amplifier and input to the laser oscillator, and may damage the laser oscillator.
In an attempt to prevent such damage caused by reflected laser light, Patent Document 1 discloses a fiber laser device including a wavelength converting fiber provided between a laser oscillator and an optical fiber amplifier, and further including a filter between the laser oscillator and the wavelength converting fiber. The wavelength converting fiber converts the wavelength of laser light having high intensity using stimulated Raman scattering. The filter transmits laser light having a wavelength emitted by the laser oscillator but blocks transmission of laser light having a wavelength obtained by converting the wavelength of the laser light emitted by the laser oscillator by the wavelength converting fiber.
In a fiber laser device having such a configuration, pulsed laser light output from the laser oscillator passes through the filter and is input to the wavelength converting fiber, but the wavelength thereof is not converted because the laser light has low intensity. Accordingly, the laser light having the wavelength as output from the laser oscillator is input from the wavelength converting fiber to the optical fiber amplifier, amplified thereby and output therefrom. Then, the laser light is directed to an object to be irradiated.
However, part of the laser light directed to the object to be irradiated may be reflected by the object and input to the fiber laser device through an output end thereof or the laser light may be reflected at the output end. In such a case, the reflected laser light is input to the optical fiber amplifier through the output end and amplified by the optical fiber amplifier. The amplified reflected laser light is input to the wavelength converting fiber. In this case, the wavelength of the reflected laser light is converted because the reflected laser light has high intensity as a result of being amplified. Then, the wavelength-converted reflected laser light is directed from the wavelength converting fiber to the laser oscillator, but is blocked by the filter before being input to the laser oscillator. According to the disclosure, it is thus possible to prevent the reflected laser light incident on the output end from being input to the laser oscillator and damaging the laser oscillator.